Schedule of Participating Mortgage Loans by Internal Credit Rating and Loan to Value (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 2,529.5	$ 2,560.4
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,322.4	$ 1,346.1
Mortgage Loans, Percent of Total	52.30%	52.60%
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,070.6	$ 1,076.8
Mortgage Loans, Percent of Total	42.30%	42.00%
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 124.1	$ 114.9
Mortgage Loans, Percent of Total	4.90%	4.50%
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 12.4	$ 22.6
Mortgage Loans, Percent of Total	0.50%	0.90%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 27.2	$ 27.3
Mortgage Loans, Percent of Total	1.10%	1.10%
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 702.4	$ 709.6
Mortgage Loans, Percent of Total	27.80%	27.70%
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,779.1	$ 1,802.6
Mortgage Loans, Percent of Total	70.30%	70.40%
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 20.8	$ 20.9
Mortgage Loans, Percent of Total	0.80%	0.80%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%